In the prior art, tubes have been coated with epoxy paint. Typically, a surface treatment is placed on the tube, and the paint surface then covers the surface treatment. Tubes are used in applications where they are exposed to corrosion, chipping, etc. Further the coating may have other characteristics that are not desirable. As an example, the tube may be bent after being formed and painted. The prior art have not always survived the bending to the extent that would be desired.
It has been known to utilize lacquer paints with plastic particle filler as a protective coating for steel sheet and strip products. However, it has not been proposed to utilize such plastic fillers in epoxy paints, and more specifically not epoxy paints for tubes.
In a disclosed embodiment of this invention, a tube is coated with an epoxy paint containing a percentage of plastic powder. The plastic particles are found in the final coating of the tube and provide several valuable characteristics. In particular, the plastic particles increase the resistance to chipping and corrosion. Also, the particles increase the ability of the tube to be bent and otherwise fabricated without flaking, cracking or damage of the coating. In summary, the plastic particles increase the strength of the coating and if necessary the thickness of the coating without compromising the adhesion of the final topcoat.
The powder-laden paint may be cured using various methods to produce the desired characteristics. Curing methods include but are not limited to induction, convection, infrared and radiant. Other variables in the control of the final coating characteristics include but are not limited to powder concentration; paint viscosity, particle size and shape, and solvents employed. One such processing configuration results with the majority of the plastic particles on the surface of the topcoat creating an electrically insulating coating which is sometimes desired. If a electrically conductive surface is desired the paint can be cured to more evenly disperse the plastic particles throughout the dry film layer.
Preferably, the coating includes approximately 20% plastic particles by weight which is mixed into a fixed viscosity paint. Preferably the viscosity of the paint is low, and on the order of 20 to 30 seconds when measured with a No. 2 Zahn Cup.
More preferably, the powder particles are very small, and on the average less than 20 microns. Under certain applications, particles up to 50 microns on average may be utilized. In one preferred embodiment, a Nylon material is used for the particles. More preferably, the material is Nylon 11 or Nylon 12.
Larger size particles may be best for thicker coatings or a particular surface. As an example, if conductivity is desired on the final tube, larger particles may be utilized as they will tend not to coat the entire outer surface. The use of higher viscosity paint mixtures may also be used to achieve these desired conditions.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.